It is standard to transport bulk materials such as grain, coal, or ore in containers that can be vehicles such as train hopper cars, barges, or bulk-carrier trucks. To transport the material as efficiently as possible it is obviously necessary to fill the containers to their maximum capacity.
This is typically done by means of a system comprising a supply of the bulk material and a batch-weigh bin for receiving the material from the supply, weighing the received material, and depositing the received material into the container. The supply is typically a very large bin filled with the material and having on its floor a closable outlet. The batch-weigh bin sits below the supply bin and above the container to be filled and it also has an outlet provided with a door or shutter. The batch-weigh bin is mounted on strain gauges or a weigh beam so that the weight of the material deposited in it can be determined accurately.
Under ideal circumstances the density of the material is known so that it is possible to calculate the weight that will fill the containers to the desired volume. When working with a relatively dense material such as ore, it is therefore possible to load the container with all the weight it can hold without there being any likelihood that too much material is put in, that is that the container is made to overflow.
With a lighter bulk material such as grain, however, or even with a material whose density varies as for instance occurs with outside storage when some of the material is wet, it is necessary to put into the container less weight than it can hold so as not to overflow the container. This is normally done calculating the maximum weight based on the predetermined volume the container can hold and the density of the material being charged into the container, since the bin is set up to measure weight so that any measurement must be converted into a weight measure. The problem with this method is that, to be safe, it is necessary to use the minimum possible density of the bulk material. Hence the containers are in general filled somewhat below their capacity which is a waste of shipping space.